Integrated circuit devices are increasingly being used in modern electronic applications such as computers. During normal operation, integrated circuit devices generate significant amounts of heat. If this heat is not continuously removed, the device may overheat resulting in damage to the device and/or a reduction in operating performance. As a general rule, the performance of integrated circuit devices is likely to improve when they are operated at lower temperatures. Hence, heat sink solutions which facilitate a lower integrated circuit operating temperature have an economic value over heat silk solutions offering higher integrated circuit operating temperatures.
Over the years, there has been a trend toward increases in the number of transistors and therefore capacitance within the integrated circuit; in turn, there has also been a trend towards increased clock frequency speeds of integrated circuit devices. These two trends have resulted in a proportional increase in the power used by the integrated circuit. Consequently, the heat generated by these devices has also increased. In order to adequately cool these high powered integrated circuit devices, heat sinks with greater cooling capacities have evolved.
Historically within the microprocessor industry, the majority of heat sink solutions have used aluminum extrusions. In aluminum extrusions, surface area aspect ratios are typically limited to a maximum ratio of 12:1.
In today's marketplace, with microprocessor solutions being offered in the 1.7 GHz clock frequency range, cooling requirements often cannot be met by the technical capabilities offered by aluminum extrusion technology. An increasingly common solution to this problem is folded-fin technology, with its low thickness range (0.004″-0.040″) and tight fin density capabilities which offer heat sink aspect ratios which can approach 40:1 and correspondingly larger surface areas for heat dissipation.
A typical folded-fin heat sink assembly comprises a base plate and a folded-fin assembly mounted on top of the base plate, the folded-fin assembly having a plurality of joined folded-fins extending upwardly from the base plate. A shroud may also be provided surrounding a substantial portion of the folded-fin assembly. The folded-fin assembly is produced by feeding strip aluminum or copper material through a set of blades which are actuated through cam action to produce its accordion-like structure.
Typically the base plate and the folded-fin assembly are made of materials which have a high thermal conductivity; materials such as aluminum (approximately 200 W/mK) or copper (approximately 400 W/mK) and, in some cases, these two components comprise the heat sink in its totality.
The presence of a shroud is desirable for a number of reasons, notable among which is that it can function as:    i) a device for capturing and supporting other required components of the assembly (e.g. spring clip attachment devices for attaching the heat sink to a support structure),    ii) a means for securing and supporting other required components (e.g. a cooling fan assembly),    iii) a means for ducting the heat sink airflow passage, thereby ensuring that the heated air does not rise and leave the heat sink prematurely, thereby decreasing its effectiveness,    iv) a means for protecting the potentially fragile nature of the folded-fin heat sink from being damaged during handling.
In these typical applications, the shroud may be made from non-thermally conductive materials such as plastic, and is typically attached to the heat sink in an operation which is downstream of the post-processing joining operation of securing the fins to the base by brazing, soldering, or epoxy bonding. As a general rule, the shroud in these typical applications is not a functional part of the thermal heat sink solution.
In the above-described typical folded-fin heat sink, special precautions must be taken in order to reduce the tendency of the fins to move or float in a random manner on the liquidus interface between the fins and the base plate, created in the post processing joining operation, which can lead to the problem of individual fins potentially being joined together. This results in an aesthetically displeasing visual component and, more importantly, results in a component which has a significant reduction in its potential thermal performance. Special precautions to avoid such a condition might typically include, for example:    i) the use of special fixturing during the process step,    ii) the use of additional and expensive components attached to the heat sink which act as a fixturing/separating device, and    iii) special upstream operations such as discrete laser welding of individual fins.
However, such special precautions are often undesirable, for the following reasons:    (i) they may result in significant additional capital expenditure,    (ii) they may result in additional component cost and weight,    (iii) they may result in adding significant unit processing weights through post processing joining operations (i.e. joining the fins to the base plate), which entail heating the overall mass up to a required temperature, and therefore can reduce process throughput significantly, and    (iv) they may result in additional labor associated with the loading and unloading of components into specialized brazing fixtures or specialized laser welding fixtures.
It is therefore desirable to provide a low cost, mass-producible folded-fin heat sink assembly which thermally exceeds the capabilities of aluminum extrusion technology, and assists in meeting the present marketplace needs.